The term head circumference (HC) refers to a measurement of an individual's occipital-frontal circumference, which is the largest circumferential measurement of the human head. HC is monitored routinely throughout infancy and early childhood. This measurement, similar to an infant or child's length and weight measurements, is plotted on a standardized growth chart rendering a percentile reading specific to that child's age and gender. If a child's head measures 75th percentile on the HC growth chart for girls ages 0-36 months, for instance, that means 75% of girls her same age have the same size or smaller head. The percentile reading is closely monitored by the pediatric primary care provider to assess the child's brain growth and development.
While genetics play an important role in head size, just as it does length and weight, an unexpected deviation from previous percentile will cue the provider to consider the cause. The first step is to question proper measurement technique and recheck. If accurate, parental head size is generally considered, as well as comprehensive neurological and developmental histories and exams conducted. A condition known as hydrocephalus, meaning water on the brain, for instance, is one explanation for a sudden increase in HC measurement. A smaller than expected measurement may be indicative that the child's brain is not developing properly.
Just like length and weight, a trained professional routinely obtains HC measurement at every well child visit throughout infancy and early childhood prior to the pediatric healthcare provider exam. Common practice involves use of a paper disposable or flexible plastic measuring tape which may coil back into a hard plastic case, a fixed loop tape in which one end overlaps the other, or folded/accordion-like tape, all which extend and retract with manual manipulation. Depending on the child's age, this measurement can be obtained with the infant lying on the exam table or infant/child sitting in the parent's lap. Either way, the nurse or medical assistant usually depends on the parent's assist to hold the infant or child's head still while he/she applies obtains the measurement. The examiner generally approaches the child from the front, extends the tape against the infant or child's occipital prominence, then wraps it around the frontal prominence to obtain a measurement. While this is a simple, non-invasive procedure, obtained HC measurements are often inaccurate. First, young children rarely tolerate this procedure. Young infants are squirmy, while older infants and toddlers often exhibit stranger anxiety and fight the procedure. To exacerbate their fear, the recoiling tape measure is often noisy and “clicks” when it extends, frightening a young child. Even in cases of a cooperative child, this procedure is cumbersome as the examiner attempts to hold the tape in place on the child's head while manually adjusting expanding the tape and maneuvering to read the measurement in centimeters. The tape easily slips off either boney prominence, resulting in an inaccurate measurement. Thus, the procedure is often repeated several times before obtaining an accurate measurement. It is a cumbersome, inefficient procedure that creates frustration for all involved, including patient, parent, examiner and provider. Further, when the same tape measure is used to measure other body parts (i.e., Elbow swelling resulting from infectious bacteria), this creates unnecessary risk for young infants and toddlers.